Almost 1.5 million Americans are diagnosed with neurological diseases that result in progressive dysarthrias. Progressive dysarthria eventually leads to mutism and is among the most debilitating effects of these diseases. Even though articulatory impairments are a major contributing factor to progressive dysarthrias, the current clinical gold standard tests to detect and track dysarthria progression are relatively insensitive to articulatory deficits particularly, in the early disease stages. Therefore, it is challenging to accurately detect and predict speech decline and thus, speech interventions remain poorly timed. There is a critical need to improve detection and tracking of articulatory deficits that impact functional speech so clinicians can improve the timing of speech service delivery. Early identification and improved tracking requires solid knowledge about articulatory impairment characteristics so they can be targeted in dysarthria assessments. Our understanding of articulatory deficits can be significantly strengthened by systematically examining articulatory performance across stimuli that challenge the articulatory motor system. To date, no systematic research efforts have been directed at identifying i) articulatory movement disturbances as a function of phonetic complexity of the speech stimuli and ii) articulatory mechanisms that contribute to progressive dysarthria across severities. The long-term goal is to optimize dysarthria assessment by improving the early detection and tracking of articulatory performance in people with progressive dysarthrias. The short-term goal of the proposed cross- sectional study is to focus on ALS and examine how phonetic complexity modulates articulatory motor performance in different dysarthria severities. Our research strategy is to use state-of-the-art speech tracking technology to capture phonetic complexity effects of single word stimuli at the kinematic level in 15 talkers each with preclinical, mild, and moderate dysarthria relative to 45 controls. The specific aims are to determine the effects of phonetic complexity on (i) articulator (tongue, lip, jaw) movement speed and distance, (ii) inter- articulator (tongue, lip, jaw) coordination, and (iii) articulator (tongue, lip, jaw) movement variability. This work is innovative because it will provide an unprecedented, cohesive picture of how the fundamental aspects of articulation change in response to phonetic complexity and dysarthria severity. The outcomes of the proposed research will have a broad and significant impact because the findings have potential to improve speech assessments for a wide range of etiologies (e.g., neurodegenerative diseases, acute stroke, developmental speech disorders) as well as for a wide range of purposes (e.g., evaluation of surgical therapies, tracking of treatment effects, tracking of disease progression). As a critical step in our translational research program, the outcomes also hold promise for leading to earlier speech interventions for people with progressive dysarthrias, a growing problem in the United States due to the aging and rising veteran population.